In order to obtain a wide viewing angle, the IPS (in-plane switching) type LCD has been developed. FIG. 9 is a schematic, exploded isometric view of a conventional IPS LCD 100. The IPS LCD 100 includes a first substrate 11, a second substrate 12 opposite to the first substrate 11, and a liquid crystal layer 15 sandwiched between the substrates 11, 12. The liquid crystal layer 15 includes liquid crystal molecules 18. A first and a second polarizers 13, 14 are formed at outer sides of the substrates 11, 12 respectively. A plurality of pixel electrodes 16 and common electrodes 17 are disposed parallel to each other at an inner surface of the second substrate 12. A first alignment layer (not shown) is disposed at an inner surface of the first substrate 11. A second alignment layer (not shown) is disposed at the inner surface of the second substrate 12, covering the pixel electrodes 16 and common electrodes 17. Original rubbing directions of the first alignment layer and the second alignment layer are parallel to each other. Long axes of liquid crystal molecules 18 adjacent to the alignment layers are approximately parallel to the first substrate 11 and the second substrate 12. Polarizing axes of the first and second polarizers 13, 14 are perpendicular to each other.
When no voltage is applied, the long axes of the liquid crystal molecules 18 maintain an angle relative to the pixel and common electrodes 16, 17. Light beams are emitted from a back light module (not shown) underneath the second substrate 12. When the light beams pass through the liquid crystal layer 15, their polarizing directions do not change, and the light beams are absorbed by the first polarizer 13. Thus the IPS LCD 100 is in an “off” state, and cannot display images.
As shown in FIG. 10, when a voltage is applied to the pixel and common electrodes 16, 17, an electric field E1 is generated between the pixel and common electrodes 16, 17. A direction of the electric field E1 is parallel to the second substrate 12, and perpendicular to the pixel and common electrodes 16, 17. The long axes of the liquid crystal molecules 18 twist to align in the direction of the electric field E1. Light beams exiting from the second polarizer 14 pass through the liquid crystal layer 15, and the polarization state of the light beams is converted to match the polarizing axis of the first polarizer 13. Thus the light beams pass through the first polarizer 13 to display images, and the IPS LCD 100 is in an “on” state.
However, before the voltage is applied, all the liquid crystal molecules 18 are aligned in the same direction. When the voltage is applied and the liquid crystal molecules 18 twist to align in the new direction according to the electric field E1, the amount of time needed for all the liquid crystal molecules 18 to twist is unduly long. This means that the response time of the IPS LCD 100 is unduly long.
What is needed, therefore, is an IPS LCD which overcomes the above-described problems.